Hydrogen peroxide-induced deacetylation of acetyl resorufin as a novel indicator reaction for fluorometric detection of glucose using only glucose oxidase

Non-quaternary oximes detoxify nerve agents and reactivate nerve agent-inhibited human butyrylcholinesterase

Government-sanctioned use of nerve agents (NA) has escalated dramatically in recent years. Oxime reactivators of organophosphate (OP)-inhibited acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) serve as antidotes toward poisoning by OPNAs. The oximes used as therapeutics are quaternary compounds that cannot penetrate the blood-brain barrier (BBB). There remains an urgent need for the development of next generation OPNA therapeutics. We have developed two high-throughput screening (HTS) assays using a fluorogenic NA surrogate, O-ethyl methylphosphonyl O-4-methyl-3-cyano-coumarin (EMP-MeCyC). EMP-MeCyC detoxification and EMP-BChE reactivation screening campaigns of ~155,000 small molecules resulted in the identification of 33 nucleophile candidates, including non-quaternary oximes. Four of the oximes were reactivators of both Sarin- and VX-inhibited BChE and directly detoxified Sarin. One oxime also detoxified VX. The novel reactivators included a non-quaternary pyridine amidoxime, benzamidoxime, benzaldoxime and a piperidyl-ketoxime. The VX-inhibited BChE reactivation reaction rates by these novel molecules were similar to those observed with known bis-quaternary reactivators and faster than mono-quaternary pyridinium oximes. Notably, we discovered the first ketoxime reactivator of OP-ChEs and detoxifier of OPNAs. Preliminary toxicological studies demonstrated that the newly discovered non-quaternary oximes were relatively non-toxic in mice. The discovery of unique non-quaternary oximes opens the door to the design of novel therapeutics and decontamination agents following OPNA exposure.

Recent advances in fluorescent probes for the detection of reactive oxygen species

Reactive oxygen species (ROS) have captured the interest of many researchers in the chemical, biological, and medical fields since they are thought to be associated with various pathological conditions. Fluorescent probes for the detection of ROS are promising tools with which to enhance our understanding of the physiological roles of ROS, because they provide spatial and temporal information about target biomolecules in in vivo cellular systems. ROS probes, designed to detect specific ROS with a high selectivity, would be desirable, since it is now becoming clear that each ROS has its own unique physiological activity. However, dihydro-compounds such as 2',7'-dichlorodihydrofluorescein (DCFH), which have traditionally been used for detecting ROS, tend to react with a wide variety of ROS and are not completely photostable. Some attractive fluorescent probes that exhibit a high degree of selectivity toward specific ROS have recently been reported, and these selective probes are expected to have great potential for elucidating unknown physiological mechanisms associated with their target ROS. This review focuses on the design, detection mechanism, and performance of fluorescent probes for the detection of singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), hydroxyl radicals ((.)OH), or superoxide anion (O(2) (-.)), a field in which remarkable progress has been achieved in the last few years.

Time-resolved enzymatic determination of glucose using a fluorescent europium probe for hydrogen peroxide

An enzymatic assay for glucose based on the use of the fluorescent probe for hydrogen peroxide, europium(III) tetracycline (EuTc), is described. The weakly fluorescent EuTc and enzymatically generated H2O2 form a strongly fluorescent complex (EuTc-H2O2) whose fluorescence decay profile is significantly different. Since the decay time of EuTc-H2O2 is in the microseconds time domain, fluorescence can be detected in the time-resolved mode, thus enabling substantial reduction of background fluorescence. The scheme represents the first H2O2-based time-resolved fluorescence assay for glucose not requiring the presence of a peroxidase. The time-resolved assay (with a delay time of 60 micros and using endpoint detection) enables glucose to be determined at levels as low as 2.2 micromol L(-1), with a dynamic range of 2.2-100 micromol L(-1). The method also was adapted to a kinetic assay in order to cover higher glucose levels (mmol L(-1) range). The latter was validated by analyzing spiked serum samples and gave a good linear relationship for glucose levels from 2.5 to 55.5 mmol L(-1). Noteworthy features of the assay include easy accessibility of the probe, large Stokes' shift, a line-like fluorescence peaking at 616 nm, stability towards oxygen, a working pH of approximately 7, and its suitability for both kinetic and endpoint determination.

Simple PbII fluorescent probe based on PbII-catalyzed hydrolysis of phosphodiester

A new fluorescent probe for PbII, p-nitrophenyl 3H-phenoxazin-3-one-7-yl phosphoric acid (NPPA), was designed and synthesized by linking resorufin (serving as a fluorophore and electron acceptor) to p-nitrophenol (serving as a fluorescence quencher and electron donor) through phosphodiester bonds. When NPPA was irradiated with light, intramolecular fluorescence self-quenching took place because of the photoinduced electron transfer from the donor to the acceptor. However, upon the addition of PbII, the phosphate ester bonds in the probe were cleaved and the fluorophore was released, accompanying the retrievement of fluorescence.

Assessment of acyl groups and reaction conditions in the competition between perhydrolysis and hydrolysis of acyl resorufins for developing an indicator reaction for fluorometric analysis of hydrogen peroxide

Perhydrolysis of acetyl resorufin (AR) was reported previously to work as a fluorometric indicator reaction for glucose determination using only glucose oxidase. However, hydrolysis of AR in blank solution rendered the working concentration range of this method less than two orders of magnitude. To exclude or at least significantly reduce this interference, acyl groups and reaction conditions in the competition between perhydrolysis and hydrolysis of various acyl resorufins were assessed. Fluorometric evaluation of reactions in the presence or absence of H202 in phosphate buffer (pH 7.5, 100 mm)-CH3CN at 25 degrees C demonstrated that in tert-butylacetyl, isobutyryl, cyclohexanecarbonyl and pivaloyl resorufins (TBAR, IBR, CHR and PVR, respectively) among 10 acyl resorufins examined here, the competitive situation was shifted in a much more favorable way to perhydrolysis than in AR, although fluorometric responses due to their H2O2-dependent deacylation were suppressed in comparison with AR. Examination of the effects of pH, components and concentrations of buffers as well as reaction temperature established reaction conditions that not only allowed perhydrolysis of each of these four compounds to prevail over hydrolysis more effectively, but also improved the H2O2-based fluorometric responses. Thus, perhydrolysis of TBAR, IBR, CHR and PVR in phosphate buffer (pH 8.0, 20 mM)-CH3CN at 25 degrees C worked effectively as fluorometric indicator reactions for H2O2 analysis, affording a calibration curve over a concentration range of three orders of magnitude. Taking sensitivity, reproducibility and the response for blank solution into consideration, PVR seemed to be the best choice as a fluorochromogen for H2O2 determination under these conditions. For H2O2 analysis at lower pH, perhydrolysis of IBR in phosphate buffer (pH 7.5, 20 mm)-CH3CN was shown to effectively function as an indicator reaction. Applicability of the fluorometric methods with PVR and IBR to blood glucose determination was also discussed, comparing with Trinder's method with phenol, 4-aminoantipyrine and peroxidase (POD).